Turkish troops and Syrian opposition forces have attacked a Kurdish enclave in northern Syria in their bid to oust from the area a US-allied Kurdish militia.

The Turkish offensive on Afrin, codenamed Operation Olive Branch, started on Saturday and has heightened tensions in the already complicated Syrian conflict, threatening to further strain ties between Nato allies Turkey and the United States.

It prompted condemnations from the Syrian government, Iran and Egypt.

France called for an emergency UN Security Council meeting to discuss the developments there and urged Turkish authorities “to act with restraint in a context where the humanitarian situation is deteriorating in several regions of Syria”.

Residents watch as a truck, part of a convoy, transporting a Turkish army tank is driven in the outskirts of the town of Kilis, Turkey, near the border with Syria (Lefteris Pitarakis/AP)

Turkish officials said the troops entered Afrin a day after dozens of Turkish jets and artillery units at the border pounded Syrian Kurdish targets.

A spokesman for the Kurdish fighters said the attack was repelled.

Turkey considers the Syrian Kurdish militia, known as the People’s Protection Units (YPG), a terror organisation and a security threat because of its affiliation with Kurdish rebels fighting in south-eastern Turkey.

The group controls Afrin, in Syria’s north-western Aleppo province, as well as a swathe of territory to the east along Turkey’s border.

The YPG also forms the backbone of the Syrian Democratic Forces, the main US ally against the Islamic State group in Syria.

US support for the Kurdish militia has been a cause of perpetual conflict between Ankara and Washington, which has backed the Kurdish militia in the fight against IS militants in eastern Syria.

There was no immediate US comment on the operation in Afrin, where it does not maintain troops, but US officials have said that the administration had appealed to Turkey not to go ahead with the offensive.

A Turkish operation there could have an impact on US operations further east in Syria, the officials said.

The operation, for which Turkey has also rallied nearly 10,000 Syrian opposition fighters, could spill into a wider Turkish-Kurdish confrontation inside Turkey. There are an estimated 8,000 to 10,000 Kurdish fighters in the Afrin district, the Turkish prime minister said.

The operation also includes air strikes on the district, threatening to create another humanitarian disaster in the region.

Mr Bali said the SDF sent reinforcements to Afrin. The YPG said meanwhile that it had destroyed two Turkish tanks.

Turkish President Recep Tayyip Erdogan has vowed to expand the offensive to Manbij, a town to the east that Kurdish forces seized from IS in a costly battle with the aid of the US-led coalition. The town has since emerged as a model for US-backed Kurdish rule of largely Arab areas.

Smoke billows from a position inside Syria, after a Turkish army artillery fired (Lefteris Pitarakis/AP)

An advance on Manbij by Nato member Turkey would strain relations with Washington, which has troops operating in the Manbij area.

Turkish troops first crossed into Syria after the Kurds captured Manbij in 2016, in part to prevent them from expanding westward and linking territory to Afrin. At least 70 Turkish soldiers were killed, most in battles with IS, which has since been driven from nearly all the territory it once held in Syria.

Syria’s government had vowed to shoot down any Turkish fighter jets over Afrin, calling it an “aggressive act”.

On Sunday, President Bashar Assad condemned the “brutal aggression” on Afrin but did not repeat the threat. He said Turkey has always supported “terrorists” in Syria.

Iran, a close ally of Assad, also condemned the Turkish assault and called on Turkey to end it.

“The continuing crisis in Afrin may boost terrorist groups again in the northern parts of Syria,” Iranian Foreign Ministry spokesman Bahram Ghasemi said, according to Iran’s official IRNA news agency.

Egypt, which maintains security co-ordination with Syria and is at odds with Turkey, also condemned the military offensive and said it threatened political negotiations.

Turkey has prepared around 10,000 Syrian fighters to storm Afrin, according to Rami Abdurrahman, director of the Syrian Observatory for Human Rights, a Britain-based monitoring group.

A Syrian commander said there were thousands of fighters positioned in Azaz, at the frontier with the Kurdish enclave, awaiting orders. Another commander said hundreds more were stationed in Atmeh, south of Afrin.